You said the bedtime routine has not changed.
BUT, she has changed. In many ways.
From this age onward, a child starts to have night-time 'fears', and nightmares.
It is developmental based.
Sometimes they cannot express that. At this young, they don't know how to fathom or analyze, all of this. A child's emotions are not even fully-developed yet at this age.
At this age, they COMMONLY have sleep tweaks. Their minds and imaginations, are changing so so much. And we cannot turn 'off' a child's imaginations or dreams or cognition.
And they do not have, at this age, keenly succinct deductive reasoning.
It is hard at this age... once things are dark.
They do get night time fears. To just anything. Even if it does not make sense to us as an adult.
Again-- At this age, they commonly have sleep tweaks. Nothing is engraved in stone.
You need to ebb and flow, as they ebb and flow in all their groping at emotions. They don't know how, yet.
Sure some may say they just try to manipulate the parent. Sure.
But for me, I KNOW if my kids are manipulating or if they are genuinely fearful or scared or anxious or need just plain ol' comfort from Mommy.
It is no big deal.
A kid WILL go through sleep phases.. .it is not finite.
They will, go through sleep difficulties, or not.
They will, change as their age juncture changes too.
It is not static.
It is not finite.
One day, they WILL go to bed... without any disturbance. At all. And then... you will 'miss' those times of them needing you.
For me, it really is no big deal if my kids get scared at night or need comfort or have a hard time sleeping sometimes or wake.
It is not a big deal.
As a child gets older... they will naturally... sleep all darn night and without waking and not calling you at all.
Your child is very young.